The present invention relates to the field of turbine engines and in particular to their lubrication.
The term “turbine engine” is used in the present context to mean any machine for converting the thermal energy of a working fluid into mechanical energy by causing said working fluid to expand in a turbine. More particularly, the working fluid may be a combustion gas resulting from the chemical reaction of a fuel with air in a combustion chamber, after the air has been compressed in a compressor that is itself actuated by the turbine via a first rotary shaft. Thus, turbine engines, as understood in the present context, comprise bypass and non-bypass turbojets, turboprops, turboshaft engines, or gas turbines, among others. In the description below, the terms “upstream” and “downstream” are defined relative to the normal flow direction of the working fluid through the turbine engine.
In order to reduce fuel consumption on multi-engine power plants, proposals have been made, in particular in French patent application FR 2 967 132 A1, to extinguish the combustion chamber of one or more engines under cruising conditions, with the engines that continue to operate thus operating at higher power levels and thereby achieving better specific fuel consumption. In order to accelerate restarting, in particular for the purpose of possible emergency restarting in order to replace or back up another power source that has failed, French patent application FR 2 967 132 A1 also proposes using an actuator device for actuating said first rotary shaft to keep said turbine and compressor in rotation for the or each turbine engine in which the combustion chamber is extinguished. Nevertheless, in such a standby mode, known as “turning mode”, the lubricant is no longer heated by heat losses from the engine, and depending on atmospheric conditions, in particular at high altitude or in cold weather, its temperature can drop rapidly to values that are very low, to such an extent that the engine is no longer properly lubricated. Unfortunately, one of the limitations on use that are inherent to such turbine engines lies in the need to have sufficient lubrication before it is possible to deliver power to the power takeoff shaft, which requires some minimum temperature for the lubricant, usually of about 273 kelvins (K) or 278 K, depending on the lubricant. It can thus be seen that, for an engine that is kept in turning mode with its combustion chamber extinguished, it is desirable to maintain at least some minimum temperature for the lubricant.